The present invention relates to a clamping device for the cylinder heads of aero engines.
In most of the Otto cycle engines fitted to light aircraft (e.g. small executive or tourist planes) and utilizing aviation type gasoline, use is made of a screw fit to couple single head assemblies, each comprising the fuel supply system for one piston, to a crankcase accommodating the connecting rods, crankshaft and compression system; each head affords an internal screw thread, and fits over a corresponding external thread cut onto a liner associated with the crankcase and constituting the relative cylinder in part.
Such an arrangement is intended principally to facilitate and expedite the frequent servicing operations carried out on each head or piston, in any location, when the plane is on the ground between flights.
Given the increasing difficulty in finding fuel for gasoline aero engines, the applicant has already envisaged and proceeded to embody an engine capable of responding to all the usual requirements of a propulsion unit of the type in question, while possessing all or practically all the features of a Diesel engine, first among which being the ability to run on the `Jet-Al` fuel in widespread use for modern passenger airliners.
In this new aero engine architecture, however, the piston-and-cylinder assembly (which incorporates the combustion chamber) is capable of considerably higher compression ratios than those of former aero engines, not least by reason of the fuel injection and compression ignition operating characteristics. With higher compression generated in the piston and cylinder assembly, and the larger bores typical of the design, significant problems are created with the plain screw fit mentioned above; in particular, the screw coupling may be forced, or at all events loosened by the stress generated during operation, thereby affecting the tightness of the combustion chamber and reducing the efficiency of the engine at altitude, which is clearly unacceptable in an aircraft propulsion unit.
Accordingly, the object of the present invention is to overcome the drawbacks in question by providing a clamping device for the cylinder head and liner assembly of an aero engine that will combine with the screw coupling conventionally adopted to ensure a faultless seal and a better distribution of the forces generated during the compression stroke, without negatively affecting the architecture of the head.